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NVAP Reference Guide - Scrapie

(Control and Eradication)

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NVAP Reference Guide: Table of Contents

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Preface

Introduction

Control and Eradication

Brucellosis

Johne’s Disease

Pseudorabies (PRV)

Tuberculosis

Transmissible Spongiform Encephalopathies

Scrapie

Bovine Spongiform Encephalopathy (BSE)

Chronic Wasting Disease (CWD)

Poultry
National Poultry Improvement Plan (NPIP)

Avian Influenza (AI)

Exotic Newcastle disease (END)

Equine Disease

Aquatic Animal

Aquatic Animal National Health Plan

Aquatic Animal Health Activities

Animal Health Emergency Management

Animal Health Emergency Management

Emergency Response Structure

National Response Framework (NRF)

National Incident Management System (NIMS)

National Animal Health Emergency Management System (NAHEMS)

Foreign Animal Disease Preparedness and Response Plan (FAD PReP)

FAD Recognition and Initial Response

National Animal Health Emergency Response Corps (NAHERC)

Notifiable Diseases and Conditions

WOAH and International Standards

Cleaning and Disinfection

Importance of Cleaning & Disinfection

Cleaning

Disinfection

Regulation of Disinfectants

Safety

Disease Surveillance

Laboratory Submissions

Animal Movement

Interstate Regulations

Interstate Movement of Cattle, Horses, Swine, Sheep and Goats

Issuing Interstate Animal Movement Documents

International Animal Movement

Issuing International Health Certificates (IHCs) for Live Animal Movement

Common Problems Observed on Certificates for Live Animal Movement
Animal Identification 

Animal Identification

Cattle Identification

Swine Identification

Equine Identification

Sheep and Goat Identification

Fowl Identification

Compliance and Regulations

Appendix

A: 9 CFR PARTS 160, 161, and 162

B: APHIS VS District Offices

C: State Animal Health Officials

D: Forms

E: Other Organizational Information with Contact Points

F: Web Sites

G: Equine Teeth and Aging

There are two types of scrapie; classical and nonclassical. Nonclassical scrapie is

also referred to as atypical, Nor98, or Nor98-like scrapie. Nonclassical scrapie

appears to occur sporadically and has occurred in sheep of all the common

genotypes and goats. It is either not transmissible or poorly transmissible under

natural conditions. Given this the scrapie eradication program focuses on classical

scrapie. Here after where “scrapie” is used it is intended to mean “classical

scrapie”. 

Scrapie is a fatal, degenerative TSE disease affecting the central nervous system of

sheep and goats. First recognized as a disease of sheep in Great Britain and other

countries of Western Europe more than 250 years ago, scrapie has been reported

throughout the world. In the United States, scrapie has primarily been reported in

the black-face meat breeds and their crosses. It also has been diagnosed in

numerous other breeds and crossbreeds including wool and hair sheep, and in goats.

At the end of FY 2016, the percent of cull sheep found positive at slaughter and

adjusted for face color was 0.001 percent with an upper confidence limit of 0.009

percent. This measure of prevalence has decreased by 99 percent since slaughter

surveillance started in FY 2003. Based on all goats sampled at slaughter through FY
2016, the prevalence of scrapie in U.S. cull goats is 0.002 percent with an upper 95

percent confidence limit of 0.004 percent.

The agent responsible for scrapie and other TSEs is smaller than the smallest known

virus and has not been completely characterized. There are a variety of theories

regarding the nature of the agent. The most widely accepted is that disease is

caused by an infectious protein, or prion, that causes the normal cellular version of

the protein to change shape such that it can no longer be degraded by the cell,

causing the protein to accumulate and damage the cell. 

The scrapie agent is extremely resistant to heat and to normal sterilization

processes. It does not evoke any detectable immune response or inflammatory

reaction in host animals. The scrapie agent is thought to be spread most commonly

from the ewe to her offspring and to other lambs in contemporary lambing groups

through contact with the placenta and placental fluids and through milk and

colostrum. Signs or effects of the disease usually appear 2 to 5 years after the

animal is infected but may take longer to appear. Sheep usually live 1 to 6 months

after the onset of clinical signs and in some cases longer, but death is inevitable. 

On the farm, veterinarians identify scrapie suspects based on the appearance of its

signs combined with knowledge of the animal’s history and signalment. Signs of

scrapie vary widely among individual animals and develop very slowly. As the result

of nerve cell damage, affected animals usually show behavioral changes, tremor

(especially of the head and neck), pruritus, and locomotor incoordination, which

progresses to recumbency and death. Early signs include subtle changes in behavior

or temperament. These changes may be followed by scratching and rubbing against

fixed objects, apparently to relieve itching. Other signs are loss of coordination,

weight loss despite retention of appetite, biting of feet and limbs, lip smacking, and

gait abnormalities, including high-stepping of the forelegs, hopping like a rabbit, and

swaying of the back end. 

An infected animal may appear normal if left undisturbed at rest. However, when

stimulated by a sudden noise, excessive movement, or the stress of handling, the

animal may tremble or fall down in a convulsive like state. Several other problems

can cause clinical signs similar to scrapie in sheep, including the diseases ovine

progressive pneumonia, listeriosis, and rabies; the presence of external parasites

(lice and mites); pregnancy toxemia; and toxins. 
Testing                        

The official test currently used for scrapie diagnosis in the United States is

immunohistochemistry. 

Histopathology, Western Blot, and ELISA may be used as supplemental tests or when

tissues are not suitable for immunohistochemistry. Histopathology is used to identify

pathological changes in the brain following necropsy. Pathological changes of

scrapie are confined to the central nervous system. The lesions are characteristically

found in the grey matter of the brainstem. They include neuronal vacuolation, other

forms of neuronal degeneration, astrocytosis, and a vacuolar or spongy alteration

called status spongiosis. Immunohistochemistry, Western Blot, and ELISA can be

used to detect the abnormal prion protein in brain or lymphoid tissues.

Third-eyelid and rectal lymphoid tissue biopsy are APHIS-approved tests for scrapie

detection in live animals. The tests use a biopsy of lymphoid tissue from the third

eyelid or rectum and IHC. Rectal biopsies are preferred over third-eyelid biopsies

because they typically have more follicles so fewer samples are read out as invalid

test due to insufficient follicles. Most collectors also find it  easier to collect rectal

biopsies compared to third eyelid biopsies. A single rectal biopsy or two third eyelid

biopsies done at the same time have a sensitivity of approximately 87 percent when

compared to the result of IHC testing on lymph node and brain. When animals over

14 months are tested, held and necropsied upon death the sensitivity of the third

eyelid is reduced to about 70 percent as would be expected due to the long

incubation period of the disease. It is likely that the rectal biopsy, if evaluated long

term, would have similar results. 

Identifying Affected Animals

Animals that are incubating the disease and may be shedding the agent are rarely

identified until the onset of clinical signs. The only absolute way to prevent an

introduction of scrapie into a flock is to prohibit all movements of sheep and goats

into a flock. Until a more sensitive, cost-effective live-animal test is available, the

risk can be substantially reduced by maintaining a closed ewe flock; by acquiring

female animals only from certified free flocks, zones, or countries; and/or by

acquiring ewes that are genetically resistant or less susceptible. 

If scrapie develops in a flock, the risk of further spread, reintroduction of the

disease, or both can be minimized through
Removal of genetically susceptible exposed sheep and exposed goats;

If all susceptible exposed animals are not removed live-animal testing and

removal of test-positive animals;

Breeding for genetic resistance;

Careful cleaning and disinfection of lambing facilities;

Improved management of animals at lambing time with particular attention to

segregating them into small groups or keeping them alone when possible,

maintaining the risk classification of animals in each group at the same level,

and removing and burying, landfilling or incinerating placenta and soiled

bedding immediately following lambing; and

When warranted by extremely valuable seedstock, employing embryo transfer,

cesarean section, or both. 

The National Scrapie Eradication Program

The National Scrapie Eradication Program has two major components: a regulatory

eradication program called the Accelerated Scrapie Eradication Program (ASEP) and

a voluntary certification program called the Scrapie Flock Certification Program

(SFCP). 

Accelerated Scrapie Eradication Program

In September 2001, the scrapie regulations were revised to require the official

identification of sheep and goats not in slaughter channels (except low-risk

commercial goats) and any sheep over 18 months of age in interstate

commerce with some exceptions. In addition, the revision required States to

implement and enforce official identification of most sheep and goats on

change of ownership intrastate in order to move sheep and goats interstate

with minimal restrictions.

APHIS provides free official sheep and goat eartags to producers and accredited

veterinarians. Call 866-USDA-TAG to request tags;

Infected sheep are identified through active slaughter surveillance, reporting of

suspect animals by producers and accredited veterinarians, testing of mature

sheep or goats that die on farm or at other locations, and live-animal testing of

higher risk animals;

Effective tracing of infected animals to their flock or herd of origin and tracing

and testing of exposed animals made possible as a result of the new
identification requirements; and

Providing effective cleanup strategies that will allow producers to stay in

business, preserve breeding stock, and remain economically viable.

APHIS provides the following assistance to owners of exposed and infected flocks or

herds that participate in cleanup plans including owners of exposed animals that

have been sold out of infected and source flocks or herds:

Indemnity for high-risk, suspect, and scrapie-positive sheep and exposed goats

that owners agree to destroy;

Genetic testing of sheep for scrapie susceptibility; and

Scrapie testing on live or dead animals 

Scrapie Flock Certification Program (SFCP)

The SFCP is a voluntary program that is open to all sheep and goat producers in the

United States. The overall objective of the SFCP is to minimize the scrapie risk of

participating flocks and herds, thereby improving the marketability of animals from

participating flocks and herds and contributing to the national scrapie eradication

program.  

The SFCP has two categories: Export and Select. The Export category has two

statuses (Export Monitored and Export Certified), and the Select category has one

status (Select Monitored). 

Export Category. The objective of this category is to certify participating flocks and

herds as scrapie free establishments through limiting the acquisition of does and

ewes from flocks of the same or higher status, annual inspections including

reconciliation of the animal inventory, official individual animal identification (ID)

requirements, recordkeeping requirements, and animal sampling requirements.

Animals from Export Certified flocks are considered highly unlikely to be infected

with scrapie, and have greater marketing opportunities both domestically and

internationally. 

Select Category. The objective of this category is enhance scrapie surveillance by

increasing the reporting of animals with clinical signs of scrapie and submission of

samples for scrapie testing. Select flocks are required to submit samples from at

least one mature animal for scrapie testing every 1-3 years, depending on the size

of the flock or herd. Participating flocks do not advance to a certified status.
All requirements of the SFCP are outlined in the SFCP program standards, available

in electronic form at: Scrapie Free Flock Certification Program

Role of Accredited Veterinarians in Scrapie Eradication Accredited

veterinarians play an integral role in the eradication of scrapie. The accreditation

standards require reporting of live or dead scrapie suspects to State and Federal

authorities. In addition to this critical role, accredited veterinarians are the

producers’ primary source of education about all aspects of the program, including

identification, recordkeeping, and movement requirements. When requested by the

producer, accredited veterinarians can apply official eartags, collect and submit

samples for official genotype testing, scrapie testing on obex, lymph node, thirdeyelid lymphoid tissue, or rectal lymphoid tissue; and issue Certificates of Veterinary

Inspection for interstate movement. Additionally, accredited veterinarians play a

very important role in educating producers about the disease and in assisting

producers with the prevention and elimination of scrapie. 

Information on the issuance of Certificates of Veterinary Inspection for sheep and

goats and on identification of sheep and goats can be found in the “Sheep and Goat”

section under the “Animal Movement” heading. Additional information on the APHIS

National Scrapie Eradication Program may be found at: National Scrapie Eradication

Program

Guidance on the scrapie regulations can be found in the Scrapie Eradication Uniform

Methods and Rules at : Scrapie Eradication Uniform Methods and Rules (271.72 KB)